1. Description of the Prior Art
Water conservation is essential in addressing water shortage caused by climate change and population increase in many parts of the world. Since water consumption in toilet flushing is an important contributor to the household water usage, manufacturers have been making better toilets using less water in a full flush than those made a few decades earlier. Meanwhile, about four out of five toilet flushes remove mainly liquid waste (such as urine and a small amount of toilet paper) from the bowl into the discharge pipe below, and they do not need a full tank of the flushable water, which is defined herein as the water volume between the normal water level in the toilet tank (when the tank has been refilled) and the flush valve seat opening (located slightly above the tank bottom) and is designed to remove a full load of solid waste (such as feces). To reduce the water consumption, the prior art has revealed a number of dual flush toilet mechanisms to provide a user with two choices—a conventional full flush to remove solid waste and a partial flush to remove liquid waste using less water than in a full flush. A large number of prior art patents related to the dual flush toilet mechanisms have been published. For example, over 140 U.S. patents are referenced in U.S. Pat. No. 7,591,027. The prior art inventions can be generally divided into seven types based on overall characteristics.
Type 1 of the prior art provides two flush valves at different heights in a toilet tank, including a lower flush valve installed near the bottom opening of the tank and an upper flush valve installed at a certain height above the tank bottom. An example is discussed in U.S. Pat. No. 3,795,016. Each flush valve is connected with a metal chain to a separate flush lever. A handle for full flush is connected to one of the two concentric shafts that at its other end is fixed to the full flush lever. Similarly, a handle for partial flush is connected to the other concentric shaft that at its other end is fixed to the partial flush lever. To activate a full flush, depress the full flush handle to raise the full flush lever and open the lower flush valve to empty the tank water above the lower flush valve seat, as in a conventional single flush toilet. To activate a partial flush, depress the partial flush handle to raise the partial flush lever and open the upper flush valve to empty tank water above the upper flush valve seat. Type 1 of the prior art mechanisms is in general much bulkier than the original flush valve assembly in a conventional single flush toilet tank. Furthermore, it would be difficult to install the Type 1 mechanism because the toilet tank needs to be removed to replace the original flush valve and overflow tube assembly. In addition, the original flush lever assembly also needs to be replaced.
Type 2 of the prior art generally uses the original flapper valve in the toilet tank and replaces the flush lever assembly with a dual flush handle and lever assembly and a float assembly with engaging mechanism. A full flush is activated by depressing the full flush handle once as in a conventional single flush toilet. Similarly, a partial flush is activated by depressing the partial flush handle for which the amount of the water allowed to drain into the bowl is controlled by the float assembly. For example, U.S. Pat. No. 5,400,445 discloses a dual flush handle and lever assembly that includes a full flush handle attached to one of the two concentric shafts, a partial flush handle attached to other concentric shaft, a housing to enclose both shafts, two levers fixed to the two flush handles respectively at one end and connected at the other end to the flapper valve by a chain or the like, stop members to limit rotation and rising of both flush levers, and a hand-turning nut to fix the shaft housing to the square opening on an upper tank wall.
The dual flush handle and lever assembly is in use with a float assembly with engaging mechanism described in U.S. Pat. No. 5,301,373, which is slidably mounted on the overflow tube in a toilet tank. The float assembly with engaging mechanism includes a cam, a vertical round shaft, a disk cam follower, a disk-shaped float, and a float stopper on the shaft. The cam is pivotally mounted at the upper end of the vertical shaft, and it is connected to the full flush lever and partial flush lever respectively by a separate chain at a different location on the cam. The lower end of the vertical shaft is linked by a chain or the like to the top of a non-buoyant flapper valve. If the original flapper valve in a toilet tank is a buoyant one, such as the one with an air chamber under the disk-shaped valve lid, it needs to be replaced with a non-buoyant flapper valve shown in U.S. Pat. No. 5,301,373.
To activate a partial flush, depress the partial flush handle to lift the partial flush lever and rotate the cam counterclockwise by a smaller angle and lower the float at a shorter distance (than in a full flush operation) below the neutral position before flushing; as the water level drops to uncover the float, the float will follow the decreasing water level and allow the non-buoyant flapper valve to reseat and stop water flow into the toilet bowl. To activate a full flush, depress the full flush handle to lift the full flush lever and rotate the cam counterclockwise by about 90 degrees, while simultaneously pushing the float to a lower level (than in a partial flush operation); the flapper valve will therefore remain open longer to allow more water to drain into the bowl below. Note that after the completion of a full flush, the cam remains in the near vertical position, and it doesn't return to its initial near horizontal position. Consequently, this can be a serious problem when trying to activate a partial flush after a full flush actuation, because depressing the partial flush handle may not be able to jerk the cam back to its initial position to perform a successful partial flush. To install the dual flush trip lever assembly and float assembly along with the engaging mechanism, the original flush lever assembly and the buoyant flapper valve in a conventional toilet have to be replaced with those described in U.S. Pat. Nos. 5,400,445 and 5,301,373.
As another example of the Type 2 prior art, U.S. Pat. No. 4,624,018 discloses a different design of a rather complicated float assembly with engaging mechanism for a dual flushing apparatus that has a full flush handle and a partial flush handle connected separately to two concentric shafts respectively. When the partial flush handle is depressed, it rotates the connected shaft until stopped by a stop member to limit the lifting distance of the flush lever so that the opening of the flapper valve is below a threshold position beyond which the flapper valve will flip open to a fully-opened position (due to buoyancy and hydrodynamic force exerted to the valve) as in a full flush. The engaging or latching mechanism subsequently keeps the lever in the raised position until the decreasing water level uncovers the float assembly to allow the lever to drop to its initial position and the flapper valve to reseat. However, the design is rather complicated with many moving parts to make the apparatus not only expensive to manufacture but also much less reliable and durable to operate. In summary, Type 2 of the prior art generally uses complex designs such as two concentric shafts and two separate levers as in U.S. Pat. No. 5,400,445 (in contrast to a single shaft and lever design of this invention discussed hereafter). More critically, the disclosed float assemblies with engaging mechanism may not work properly, and the manufacturing cost is relatively high. However, the installation is not difficult, because there is no need to remove the toilet tank during installation.
Type 3 of the prior art provides a dual flush handle and lever assembly to replace the original flush lever assembly in a conventional single flush toilet, while using the original flush valve and overflow tube assembly. For example, U.S. Pat. No. 3,988,786 reveals a dual flush mechanism, including a full flush handle attached to a hollow shaft that is connected at the other end to a flush lever, a partial flush handle attached to a smaller concentric shaft that is inserted inside the hollow shaft and is bent at the other end to form a crank located under the same flush lever, and stopping members to limit the rotation of the flush lever and the crank. To activate a partial flush, depress and hold down the partial flush handle to partially open the flush valve below the point of buoyancy and manually control the duration of valve opening. Releasing the partial flush handle will allow the flush valve to reseat and terminate water flow while using less water than in a full flush. Depressing the full flush handle once will activate a full flush as in a conventional single flush toilet. Type 3 of the prior art is easy to install by replacing only the original flush lever assembly. However, it would take a while for the user to get used to actuating a partial flush by holding down the partial flush handle until the waste is flushed out of the toilet bowl.
Type 4 of the prior art uses partition walls to divide water in a toilet tank into two compartments for which the access to the tank draining discharge pipe is controlled by valves that are opened by a dual flush handle and lever assembly. A partial flush is activated by depressing the partial flush handle to lift and open the flush valve of a designated compartment to drain its water into the bowl below. A full flush is activated by depressing the full flush handle to open the flush valves of both compartments to drain the tank water into the bowl. For example, see U.S. Pat. No. 3,487,476. Type 4 of the prior art would have limited applications, because the partition walls for the compartments have to be custom-made to fit inside toilet tanks of various inside dimensions, which are manufacturer-dependent and also model-dependent for the same manufacturer. Furthermore, installation of the Type 4 device requires the removal of the original flush valve and overflow tube assembly, and professional plumbing skill would likely be needed.
Type 5 of the prior art uses a non-buoyant flapper valve that has no air chamber and is enhanced with a weight so that it will quickly sink to the valve seat and shut off water flow into the toilet bowl, when the depressed flush handle is released by the user. There is no threshold of valve opening beyond which the weighted non-buoyant valve would uncontrollably flip to a widely open position. The water consumption of a flush is manually controlled by the duration of holding down the flush handle. In U.S. Pat. No. 4,293,964, a weighted non-buoyant flapper valve is used to replace the original flapper valve in a conventional single flush toilet. A flush is activated by continuingly depressing the flush handle until the toilet bowl is cleared of the waste. Since it takes less water to remove the liquid waste than the solid waste from the bowl, the user will release the handle earlier and therefore only a fraction of tank water is used in flushing out the liquid waste. Type 5 of the prior art mechanisms is easy to install by replacing only the original flapper valve in a conventional single flush toilet. But it is rather inconvenient to hold down the flush handle and manually control the flush duration.
Type 6 of the prior art uses a mechanical or electric timer with a drive shaft to control the time duration for a flush valve to stay open in a partial flush or in a full flush. For example, U.S. Pat. No. 4,014,050 describes a timer-controlled, dual flush toilet apparatus that is designed for a vertically sliding bulb valve instead of the pivotally-mounted flapper valve. To activate a partial flush, depress a partial flush handle to lift the flush valve and rotate the drive shaft of the timer for approximately 22.5 degrees; after the partial handle is released, a timer-driven linkage will push downward and reseat the bulb valve in about 2.5 seconds. Similarly, a full flush is activated by depressing the full flush handle to lift the flush valve to a higher elevation and rotate the timer drive shaft for approximately 45 degrees; after releasing the full flush handle, the timer-driven linkage will reseat the bulb valve in about 5 seconds. To install the apparatus, the original flush lever assembly of a toilet tank needs to be replaced with the timer-controlled drive shaft, and the original pivotally-mounted flapper valve needs to be replaced with a vertically-sliding bulb valve. More critically, Type 6 of the prior art requires the use of a timer that is relatively expensive and introduces an unattractive appearance outside the toilet tank. However, installation is not difficult.
Type 7 of the prior art discloses a dual flush mechanism activated by two spring-loaded push buttons that are vertically mounted on the top lid of a toilet tank to operate a full flush and a partial flush respectively. Pushing either button will lift and open a vertically sliding, disk-type flush valve away from its valve seat in a cylindrical structure that also contains a float assembly. An example is given in U.S. Pat. No. 6,785,913, in which the float assembly is concentrically attached to the stem of the flush valve and is shaped like an inverted cup trapping air inside. Each push button is connected to a separate vertical rod that touches one end of a nearly horizontal lever below, and the lever is hinged at the middle with the other end linked to the valve stem. Push either button will thus depress the lever and lift the disk-type flush valve away from the valve seat to start flushing by draining tank water into the toilet bowl below. A key feature is that pushing the full flush button will lift the flush valve and the float assembly to a level where the float assembly is buoyant, while pushing the partial flush button will lift the flush valve to a lower level where the float assembly is not buoyant. As a full flush button is depressed and then released in a full flush activation, it will take a longer time (than in a partial flush activation) for the flush valve to move downward with the decreasing water level until it reseats to stop water flowing into the toilet bowl. To activate a partial flush, depress and release the partial flush button to lift the flush valve to a lower level (than in a full flush operation) where the float assembly is not buoyant, and it therefore takes less time for the flush valve to move downward and reseat than in a full flush operation. Consequently, less water is consumed in a partial flush than in a full flush.
Type 7 of the prior art is easy to operate as long as it is top mounted on the lid of a toilet tank. Since most of the existing toilets have the built-in hole on either the front wall or a side wall of the tank, the prior art mechanism described in U.S. Pat. No. 6,785,913 is not applicable and cannot be used to retrofit these toilets, not to mention that its installation would be difficult and involved with the replacement of the original flush valve and overflow tube assembly and the flush lever assembly. Although modifications may be made to allow the two spring-loaded push buttons to be horizontally mounted on either the front wall or the side wall of a toilet tank and an adapter may be added to mate with the original flapper valve seat, it would be rather inconvenient for a user to operate the modified dual flush mechanism by depressing a horizontally mounted, spring-loaded push button from most likely a standing position. A variation of Type 7 mechanisms uses a conventional flush handle instead of two push buttons; a full flush is activated by depressing the handle, while a partial flush is activated by pulling the handle upward and rotating it in other direction. But it is inconvenient for the user to pull the handle upward to activate the partial flush. In addition, there are two constraints in retrofitting a conventional single flush toilet with a Type 7 mechanism. First, the inside height of the toilet tank must be large enough to accommodate the height of the Type 7 mechanism and the existing overflow tube has to be tall enough to permit a sufficient water level in the toilet tank for partial flush to work properly. Second, finding replacement parts to repair a malfunctioned Type 7 mechanism could be a problem, unless the user is willing to replace the entire mechanism at a high cost. In contrast, replacement parts for the conventional single flush toilets are readily available, and it is rather inexpensive and easy to replace a leaking flapper valve or a flush lever assembly.
In conclusion, many prior art devices are expensive to manufacture (for example, using two concentric shafts and two flush levers, and/or complex floats with engaging mechanism), difficult to install (removing the toilet tank to replace the flush valve and overflow tube assembly), expensive to repair a leaking flush valve, unreliable to operate (due to complex designs with too many moving parts), or inconvenient to operate (pushing a spring-loaded push button installed on the toilet front or side wall, or manually controlling the duration of a flush by holding down a flush handle until completion). These deficiencies may have contributed to the fact that the overwhelming majority of the U.S. households still use the conventional single flush toilets, without the benefit of a partial flush option to reduce the unnecessary water and energy consumption.
2. Advantages of the Present Invention
The present invention provides an innovative dual flush device that uses a single shaft and a single lever to work with the original flapper flush valve. The present invention also provides an innovative float assembly that can operate either with the innovative dual flush device or with the original single flush lever assembly in a conventional toilet. Compared to the prior art mechanisms (Types 2 and 3 in particular), the innovative device and float assembly are simpler in design and inherently reliable to operate, less expensive to make, and among the easiest to install. The invention provides three choices to the user to achieve a full flush and a partial flush in a toilet while using the original flapper flush valve: (1) installing only the dual flush device; (2) installing the dual flush device and a float assembly; or (3) installing only a float assembly (while using the original single flush lever assembly). The only hardware that needs to be replaced in a conventional single flush toilet is the flush lever assembly for the first two choices and none for the third choice. Installation of any of the three choices can be readily made by homeowners without hiring a professional plumber.